Acronyms used in this document are expanded below following the detailed description section.
Recent expansion in wireless traffic volume will require the network operators to continue increasing their wireless capacity. One promising technique is to use license exempt frequency spectrum, sometimes also termed unlicensed band(s) or shared band(s). Examples of such license exempt bands include the ISM band in which IEEE 802.11 type networks (hereafter, WLAN) currently operate, and also what is known as television whitespaces TVWS, which is a very large chunk of spectrum.
This is not a simple task in that since the spectrum is license exempt it will be in simultaneous use by different users operating according to different RATs such as LTE and WLAN. Recent discussions in the 3GPP indicate the solution lies in better cooperation between the LTE and WLAN systems for the case in which different users operating under these different RATs are operating in the license exempt spectrum.
FIG. 1 illustrates in general the concept of carrier aggregation in the LTE system. The whole bandwidth is divided into multiple component carriers. Each UE in the cell will be configured for one primary component carrier or PCC. If a UE is not capable of CA operation it will be assigned a single CC that is backward compatible with 3GPP Release 8. CA-capable UEs are assigned one PCC and may be configured also with one or more secondary CCs or SCCs. Relevant to some embodiments of these teachings one of those SCCs may utilize the license exempt frequencies. While each CC of FIG. 1 is backwards compatible with Release 8, that is but one example and in different CA deployments the bandwidths of the CCs may differ and not all need be backward compatible, and in fact a SCC in the license exempt band will not be backward compatible with Release 8.
Prior art approaches to relieving traffic from the licensed spectrum was to have the UE offload some of its traffic to a WLAN access point, which of course required that the offloading UE have both a LTE and a WLAN radio. Whether or not the UE remains attached to the LTE system in this scenario, WLAN simply cannot support certain features such as handing over an ongoing voice over IP call to a LTE system, meaning there will either be a service interruption or the traffic must be filtered by type before being subject to WLAN offloaded. So for unlicensed band offloading it is desirable to deploy LTE to ensure service continuity, reduce the operator cost of deploying multiple systems, reduce the need to support multiple radio technologies in the handset/UE, and take advantage of LTE-Advanced features that increase its capacity and throughput such as for example carrier aggregation, cooperative multipoint transmissions CoMP, and enhanced inter-cell interference coordination eICIC. Additionally, deploying only LTE will provide better spectral efficiency and control signal optimization compared to LTE and WLAN separately. In-device coexistence is also better with LTE-only deployment.
But LTE is not designed for unlicensed deployment, and even so there is no exclusive control over the license exempt spectrum by the LTE network which means there may still be other UEs operating in that spectrum on another RAT such as WLAN. Some solutions deploy a coexistence manager to actively coordinate among the various RAT operators utilizing the license exempt band as to who will have temporary rights to which channels. As will be detailed below, these teachings take a different course which requires no such active coordination among the various RATs.